gador/nixpkgs
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

splice: replace listToAttrs+map with mapAttrs

Browse Source 
listToAttrs forces every list element to extract `.name`, calling merge
eagerly for the entire union of attribute names (~60k). mapAttrs already
knows the keys; the lambda is only invoked when a key is selected,
letting the 99.7% unforced ones stay as untouched thunks.

NIX_SHOW_STATS delta on pkgsCross.aarch64-multiplatform.hello.drvPath:

  nrFunctionCalls:  567,512 -> 507,404   (-10.6%)
  nrThunks:         613,138 -> 552,356   (-9.9%)
  sets.number:      158,787 -> 98,339    (-38.1%)
  list.elements:    295,085 -> 174,189   (-41.0%)
  gc.totalBytes:      117.5M -> 111.7M   (-4.9%)

Repro:

  NIX_SHOW_STATS=1 nix-instantiate --eval \
    -E '(import ./. {}).pkgsCross.aarch64-multiplatform.hello.drvPath' \
    2>stats.json >/dev/null
  jq . stats.json
This commit is contained in:
zimbatm
2026-04-04 14:18:29 +02:00
parent d8c4c60db8
commit 6ae8efaf5f
1 changed files with 34 additions and 35 deletions
Download Patch File Download Diff File Expand all files Collapse all files
pkgs/top-level/splice.nix
+34 -35
View File
@@ -31,43 +31,42 @@ let
# The same pkgs sets one probably intends
// inputs.buildHost
// inputs.hostTarget;
merge = name: {
inherit name;
value =
let
defaultValue = mash.${name};
# `or {}` is for the non-derivation attsert splicing case, where `{}` is the identity.
value' = mapCrossIndex (x: x.${name} or { }) inputs;
# perf: mapAttrs defers merge calls until a key is selected, avoiding
# ~60k eager closures that listToAttrs+map would create.
merge =
name: defaultValue:
let
# `or {}` is for the non-derivation attsert splicing case, where `{}` is the identity.
value' = mapCrossIndex (x: x.${name} or { }) inputs;
augmentedValue = defaultValue // {
__spliced = lib.filterAttrs (k: v: inputs.${k} ? ${name}) value';
};
# Get the set of outputs of a derivation. If one derivation fails to
# evaluate we don't want to diverge the entire splice, so we fall back
# on {}
tryGetOutputs =
value0:
let
inherit (builtins.tryEval value0) success value;
in
getOutputs (lib.optionalAttrs success value);
getOutputs =
value: lib.genAttrs (value.outputs or (lib.optional (value ? out) "out")) (output: value.${output});
in
# The derivation along with its outputs, which we recur
# on to splice them together.
if lib.isDerivation defaultValue then
augmentedValue
// spliceReal (mapCrossIndex tryGetOutputs value' // { hostTarget = getOutputs value'.hostTarget; })
else if lib.isAttrs defaultValue then
spliceReal value'
else
# Don't be fancy about non-derivations. But we could have used used
# `__functor__` for functions instead.
defaultValue;
};
augmentedValue = defaultValue // {
__spliced = lib.filterAttrs (k: v: inputs.${k} ? ${name}) value';
};
# Get the set of outputs of a derivation. If one derivation fails to
# evaluate we don't want to diverge the entire splice, so we fall back
# on {}
tryGetOutputs =
value0:
let
inherit (builtins.tryEval value0) success value;
in
getOutputs (lib.optionalAttrs success value);
getOutputs =
value: lib.genAttrs (value.outputs or (lib.optional (value ? out) "out")) (output: value.${output});
in
# The derivation along with its outputs, which we recur
# on to splice them together.
if lib.isDerivation defaultValue then
augmentedValue
// spliceReal (mapCrossIndex tryGetOutputs value' // { hostTarget = getOutputs value'.hostTarget; })
else if lib.isAttrs defaultValue then
spliceReal value'
else
# Don't be fancy about non-derivations. But we could have used used
# `__functor__` for functions instead.
defaultValue;
in
lib.listToAttrs (map merge (lib.attrNames mash));
builtins.mapAttrs merge mash;
splicePackages =
{